The ventilation air change rate is the rate that air enters or leaves a building, expressed as air changes per hour (ac/h).
DEAP requires an estimate of the air change rate to calculate the ventilation heat loss rate (expressed in W/K) and its effect on the overall heating requirement. The ventilation rate depends on factors including permeability of materials and inadvertent gaps and openings in the structure. These factors contribute to background air infiltration or leakage characteristics and ventilation features intentionally specified and provided in the dwelling.
The air infiltration rate can be assessed either from a permeability test (also called an air leakage pressure test) see here, or, in the absence of a pressure test, using the ’structural air tightness‘ section of DEAP. Pressurisation tests are completed with all designed ventilation openings, flues, fans etc. sealed and inoperative. This component of overall air change rate represents only background dwelling air leakage.
DEAP uses the numbers of chimneys, extract fans, open flues, passive vents and flueless combustion room heaters to determine the contribution to overall air change rate from individual ventilation features (‘openings’, including fans) intentionally provided in the dwelling. These openings are entered in DEAP using the guidance below, regardless of whether there is a pressurisation test carried out or not. The contribution of designed ventilation features is given in Table 3.1 below.
| Opening type | Ventilation rate (m3/h) |
|---|---|
| Chimney | 40 |
| Open flue | 20 |
| Fan (intermittent) | 10 |
| Passive vent | 10 |
| Flueless fixed combustion room heaters1 | 40 |
The effect of sheltered sides on ventilation rates is addressed here.
The overall ventilation air change rate is adjusted to reflect the type of ventilation provision:
Part F of the Irish Building Regulations details the ventilation requirements for dwelling design and construction. Table 3.2 summarises the formulas used to calculate the Effective air change rate for the different ventilation provisions.
| Ventilation System | Effective air change rate |
|---|---|
| Natural ventilation |
If IR <= 1 ac/h: EACR = 0.5 + (IR)2 x 0.5 Otherwise: |
| Positive input ventilation from loft |
If IR <= 1 ac/h: EACR = 0.5 + (IR)2 x 0.5 + 20/V Otherwise: EACR = IR + 20/V |
|
Whole house extract ventilation or Positive input ventilation from outside |
EACR = MAX(0.5, IR + 0.25) |
| Balanced whole-house mechanical ventilation without heat recovery | EACR = IR + 0.5 |
| Balanced whole-house mechanical ventilation with heat recovery | EACR = IR + 0.5 x (1- HEE/100) |
| Exhaust air heat pump | EACR = MAX(0.5, IR + 0.5 * (0.5 * Fmv) ) |
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Where;
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